This invention relates to the formation of connections to a component for use in an electronics assembly. The connections may be mechanical, electrical or both. As used herein, the term "component" shall be applicable to parts of an assembly which modify and electrical signal, such as resistors, capacitors, diodes, transistors and integrated circuits, and to parts on which components are mounted or which serve to interconnect components, which may often be referred to generally as substrates, for example a printed circuit board as used for surface mounting of components.
Electronics assemblies of interconnected components, typical of the type with which the present invention is concerned, generally comprise a substrate component such as a printed circuit board on which other components are mounted. A component may have a small number of contacts for connection to contacts on one or more other components, for example it may have four contacts or less as in the case of a capacitor or a resistor, or it may have a large number of contacts, for example more than four, as in the case of an integrated circuit in a leadless ceramic casing. In case of complicated integrated circuits, especially those which have for example 32 contacts or more, the component that is mounted on the substrate may be a carrier on which the integrated circuit itself is mounted, such as a ceramic leadless chip carrier.
As the space occupied by individual components on a substrate component is gradually reduced as a result of miniaturization of the components, the density of contacts on the components increases. It is important to ensure that conductive material that is used to form connections between components does not also form unwanted connections between contacts. Particularly as the density of contacts increases, it becomes important to ensure that any debris remaining from making connections between components is removed. Furthermore, debris from the connections, whether conductive or not, can often be corrosive.
Solder is a commonly used material for making connections between components. When making a solder connection, it is important to ensure that excess solder and flux residues do not contaminate the connection area and, in particular, do not form unwanted connections between contacts. It is desirable therefore to leave a space between the bodies of components which are to be connected in order to be able to clean the connection area of any unwanted material. Furthermore, such a space enables the connection area to be inspected to determine whether the quality of the solder connection is satisfactory, as well as to determine whether all unwanted material has been removed.
U.S. Pat. No. 4,705,205 discloses a method of forming a connection between components, using elongate preforms of solder material which, when heated, retain their preform shape. This retention of shape may be achieved by supporting the solder by means of a support strand or tape which is disposed helically about the outside of the solder preform. The preforms are positioned so that their longitudinal axes extend perpendicularly from the surface of each of the contacts which they interconnect. This arrangement has been found to facilitate cleaning and inspection of the areas of the connections between the preform and the contacts. Furthermore, it has the advantage that the connections between the components are resilient, and are therefore able to withstand stresses arising from differences in thermal expansion of the interconnected components. However, it has been found that the small size and unstable orientation of the preforms can make correct manipulation of the preforms difficult.
U.S. Pat. No. 4712721 discloses a system for delivering solder preforms, in which preforms are disposed in apertures in an elongate tape. When the preforms are columnar, they are positioned so that their axes are parallel to the plane of the tape.
U.S. Pat. No. 4,402,450 discloses a method of bonding to a contact, by means of a composite member comprising a hard element encased in a quantity of solder. The solder can form a connection to the contact, and the hard element acts as a spacer defining a desired minimum distance between the contact and another component. This arrangement has the disadvantage that the distance between components is controlled solely by the thickness of a hard element. This means that the arrangement requires a different hard element for different desired spacings, and is somewhat less capable of tolerating an array of contacts that is not exactly planar. Furthermore, notwithstanding the fact that they provide a spacing between connected components, connections made by the disclosed method are not particularly resilient, since the spacing is provided by a hard, inflexible element.